Are UVs important for importing blender mesh into Unreal Engine 4?
The get the most of Unreal you should create a UV map for texturing and non-overlapping Light map UV for unreal to bake cached light and shadow information.

You can use the Smart UV project operator ("U" in edit mode) to quickly get a non overlapping UV map. You can then let Unreal create the Light map UV from this (on import or on the Static mesh asset) based on this.

I would however recommend you to get into manually creating your UV maps in a more controlled way. Texturing/UV-mapping should be considered as an important step as modelling.

Is it necessary? No.

Is it important? Yes (depending on what your ambitions are).